sigh. Those who believe this is earth's natural cycles repeating need to look again. When the earth changed in the past it happened slowly. The natural long term cycle is very slow cooling right now and for the next 23,000 years. (Look up Milankovitch cycles). What has happened in the past 100 years is nothing like previous climate changes. Likewise, the climate has previously tracked with the sun's intensity but again it's different now. The sun tends to work in 11 year cycles. There was a solar maximum in 1980 and the sun has been decreasing in intensity since then but warming has continued. This year so far is the 5th warmest ever recorded and the sun is near a minimum.
There is no known natural explanation for the rate of global warming over the past century or two. The warming is not not not not like any change ever before on earth. Something different and the only explanation that fits the data is increased greenhouse gasses. And we know those greenhouse gasses came from burning fossil fuels and forrests -- we know that by the mix of isotopes.
There is absolutely no natural explanation for global warming. The Milankovitch cycles should be causing cooling. The solar intensity should be causing cooling. The Pacific currents should be causing cooling. But we continue to get warming DESPITE the natural forces. Once the sun cycles towards a maximum, and/or once the Pacific converts back to an El Nino pattern and the strongest natural cooling forcings are removed, the warming will accelerate. That could be as early as next year (building on the 5th warmest year) or as late as 8 years from now.
But yeah, man made greenhouse gasses are a real problem